Discovering the unexpected breadth of stem cell plasticity opens a new conceptual front to treating a wide range of diseases. A major block to exploiting this potential rests in the inability to control what happens to a cell after it has been transplanted. Here we propose to characterize the developmental potential of human hemopoietic cells, and to develop a method that will allow for the pharmacologically controlled in situ expansion of cells that have transited from hemopoietic to non-hemopoietic tissues, using liver as a model. Our approach involves expressing a protein that induces cell growth in the presence of a chemical dimerizing agent. In Specific Aim I we will test the developmental potential of human hemopoietic cells. We will study autopsy tissues taken from female recipients of male bone marrow cells to determine whether male cells contribute to various non-hemopoietic tissues. In Specific Aim 2 we will test whether genetically modified hemopoietic cells retain hepatocyte potential. Bone marrow from male mice will be transplanted into female recipients who will then be analyzed for hepatocytes arising from the male donor. In Specific Aim 3 we will construct and test vectors for expanding marrow derived hepatocytes. In Specific Aim 4 we will use chemical dimerizing agents to expand marrow-derived hepatocytes, in vivo.